Image reading devices, often referred to as book scanners, have become commercialized. These devices generally include an image sensing system disposed above a document table so as to create an open space several tens of centimeters in height between the document table and the image sensing system. To read a bound document such as a book, magazine or the like (hereinafter referred to as "book document"), the open faced book document is placed face upward on the document table. When the start key is turned ON, the illumination lamp is activated and the sensing system starts scanning the document surface (viewing surface). As the viewing surface is scanned, the read image is sequentially output to an external device such as a printer or a storage device. When the external device is a printer, the copy image may be printed in real time as the document is scanned. Because the document is placed face upwards on the document table, the efficiency of the reading operation is improved because the pages of a book document can be turned without lifting the document from the document table.
Because the pages of an open book tend to curl or close, book documents, unlike sheet documents, must often be pressed along the edges of the viewing surface in order to maintain an open condition for scanning. In such instances, the book scanner output image may include an image of the fingers and hands of the user in addition to the document (hereinafter referred to as "extraneous object images such as fingers"). Because images of extraneous object images such as fingers are undesirable, such images must be removed before the final scanned image is stored or output. Conventionally, the extraction of extraneous object images such as fingers from a read image is accomplished by discriminating density and color pixels in the scanned image. Such methods include, for example, methods to extract an image comprised of pixels above a constant density by checking the pixel density of an object of the document margin region (white region), and methods to extract flesh colored images from an image obtained by color image sensing (See e.g., U.S. Pat. No. 5,377,019).
A problem arises in the conventional system when scanning areas that are inclined relative to the scanner. Conventionally, when an inclined area is present, such as the finger of a user, the illumination light is positively reflected by the inclined surface of the object and is thus highlighted. Because the area which is highlighted is brighter than the background of the document (i.e., has a color the color of the illumination light), the shape of the object cannot be accurately detected by either density or color. Additionally, problems can arise when attempting to extract extraneous objects based on color discrimination especially when other factors such as manicures and the like affect the color of the object.